Suction Filter for an Automatic Transmission

ABSTRACT

A filter assembly includes a filter housing including an inlet, through which hydraulic fluid enters the housing, and an outlet, through which hydraulic fluid exits the housing, valve housing containing a bypass valve located adjacent the inlet in a chamber, the valve including an orifice that opens and closes in response to differential pressure across the valve, and a screen secured to the valve housing and covering the orifice, the screen having a fine mess for removing contaminants from the fluid that flows through the valve.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a filter assembly and, inparticular, to a filter for removing contaminants in automatictransmission fluid (ATF) contained in an oil pan.

2. Description of the Prior Art

Hydraulic fluid, which circulates continuously through an automatictransmission and an external oil cooler, reenters a transmission oil panfrom the cooler through a filter, whose purpose is to removecontaminants entrained in the fluid. A hydraulic pump is supplied withfluid from the outlet of the filter. A bypass valve may be arranged inparallel flow path with a filter element such that the valve opens andcloses in response to differential pressure across the valve.

When the valve is open, however, the filter is bypassed, therebypotentially allowing large contaminants to reenter and recirculatethrough the transmission.

During cold temperature operation when the valve is open, air may enterthe filter assembly and accumulate in large bubbles, which exit thefilter and enter the intake of the pump, thereby causing slug-like fluidflow or spikes, which can produce pressure instability downstream of thepump and adversely affect the pump prime.

Undesired high pressure differential across the valve, caused by coldtemperature operation and restrictions in the flow path leading to thevalve inlet, may cause excessively long periods when the bypass valve isopen and the filter is inoperative.

A need exists in the industry for a filter that avoids bypass valveinstability due to fluctuations in pump suction flow, excessivedifferential pressure across a bypass valve, and air entrapment in thehousing of a fluid filter.

SUMMARY OF THE INVENTION

A filter assembly includes a filter housing including an inlet, throughwhich hydraulic fluid enters the housing, and an outlet, through whichhydraulic fluid exits the housing, valve housing containing a bypassvalve located adjacent the inlet in a chamber, the valve including anorifice that opens and closes in response to differential pressureacross the valve, and a screen secured to the valve housing and coveringthe orifice, the screen having a fine mess for removing contaminantsfrom the fluid that flows through the valve.

The a channel includes a second inlet communicating with the chamber andlocated adjacent the valve, a second outlet communicating with theoutlet of the valve housing, and a length connecting the second inletand second outlet, the channel increasing in elevation as distance fromthe second inlet along the channel length increases.

When valve is open during cold temperature operation, air thataccumulates in the valve passes along the channel in small, dispersedbubbles and enters the pump intake, thereby avoiding bypass valveinstability due to fluctuations in pump suction flow and loss of pumpprime.

To minimize the length of time that the bypass valve is opened duringperiods when the ATF temperature is low, the valve is locatedimmediately adjacent the inlet 18, where the valve is most exposed torelatively warm ATF flow returning to the oil pump. The valve housing isrounded at its end to create an unrestricted flow path that promotesflow of fluid toward the valve and filter housing inlet.

The scope of applicability of the preferred embodiment will becomeapparent from the following detailed description, claims and drawings.It should be understood, that the description and specific examples,although indicating preferred embodiments of the invention, are given byway of illustration only. Various changes and modifications to thedescribed embodiments and examples will become apparent to those skilledin the art.

DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood by reference to thefollowing description, taken with the accompanying drawings, in which:

FIG. 1 is a side view of a filter assembly including suction filterelement and bypass valve located in the oil sump of an automatictransmission;

FIG. 2 is bottom view of the filter assembly of FIG. 1;

FIG. 3 is an end view of the filter assembly of FIG. 1; and

FIG. 4 is a side view of a filter assembly showing a channel containingair bubbles.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The suction filter assembly 10 shown in FIG. 1 includes a filter housing12, filtration media 14 and pressure bypass valve 16. Filtration media14 is directly molded to filter housing 12 and separates a housing inlet18 and a housing outlet 20 so that all of the ATF i.e., transmissionfluid, that enters though through the inlet also passes through media 14and outlet 20 when valve 16 is closed. Filtration media 14 is able tofilter small particulate matter entrained in the ATF.

The pressure bypass valve 16 is a normally-closed check valve having aball 22 that is biased by a spring 24 toward contact with a seat 26,formed with an orifice 28. Ball 22 and spring 24 are located in a valvechamber located at a higher elevation than seat 26. Valve 16 closes whenball 22 contacts seat 26. Valve 16 opens when ball 22 moves upward outof contact with seat 26 against the force of spring 24 due todifferential fluid pressure across the valve.

Filter outlet 20 is located in the suction inlet 30 of a transmissionpump. A seal 32, fitted into an annular space between the filter outlet20 and pump inlet 30, prevents leakage of ATF.

Filter inlet 18 is located near the lowest point of the transmissionsump 34, called an oil pan, and below the elevation of the surface ofthe ATF in the oil pan 34.

To prevent ingesting air while valve 16 is open and bypassing ATF frominlet 18, valve housing 36 is provided with a small vent hole 38 locatedat the top of valve cavity 40. Air entrained in ATF that accumulates invalve cavity 40 can escape through the hole 13. To improve the escape ofair from valve cavity 40, valve seat 26 has the form of a truncated conesuch that the vent hole 38 is located at the base of the cone and abovethe elevation of the valve orifice 28.

To minimize the length of time that bypass valve 16 is opened duringperiods when the ATF temperature is low, valve 16 is located immediatelyadjacent filter inlet 18 where the valve is most exposed to relativelywarm ATF flow returning to the oil pump.

As FIG. 2 illustrates, valve housing 36 is rounded at its end to createan unrestricted flow path that promotes flow of fluid in sump 34 towardbypass valve 16 and filter housing inlet 18.

To reduce excessive flow restriction through bypass valve 16 during coldtemperature operation, as shown in shown FIGS. 1-4, the valve orifice 28is covered by a screen mesh 42, which has the form of a spherical dometo maximize the surface area of the screen. To further maximize the areaof screen 42 the area of its surface covers the rounded portion of thehousing 36, where valve 16 is located and not only the area of thevalve. Molded ribs 44, formed in valve housing 36, follow the sphericalshape of screen 42 and support the screen against collapsing due tofluid pressure. Screen 42 filters large particulate matter carried inthe ATF when valve 16 is open and bypassing fluid through the valve.

To reduce pressure spikes at the suction pump due to valve 16 rapidlyopening and closing under pulsing suction flow conditions, bypass valve16 is located downstream and spaced far from the filter assembly outlet20, to ensure maximum differential pressure between filter outlet 20 andvalve inlet 28. This location tends to cause filter housing 12 to act asan accumulator, thereby attenuating and dampening pressure spikes.

To prevent the ability of air that might accumulating downstream ofbypass valve 16 or in the filtration media 14 from exiting through thefilter outlet 20 and entering the pump inlet in a large bubble, filterhousing 12 is formed with a slopped air channel 46 or multiple sloppedchannels, which extend from the area of bypass valve 16 to the filterassembly outlet 20. The air channel 46 merges with outlet 20 through anopening 48 at the highest elevation of the slopped channel 46. Insteadof air entering outlet 20 in a large bubble, air that may accumulateabove bypass valve 16 is divided into small bubbles 50 at the entrance52 to channel 46. The small bubbles move rightward in he channel 46,pass through opening 48 and exit through outlet 20 as small bubbles.

In accordance with the provisions of the patent statutes, the preferredembodiment has been described. However, it should be noted that thealternate embodiments can be practiced otherwise than as specificallyillustrated and described.

1. A filter assembly for an automatic transmission, comprising a filterhousing including an inlet, through which hydraulic fluid enters thehousing, and an outlet, through which hydraulic fluid exits the housing;valve housing containing a bypass valve located adjacent the inlet in achamber, the valve including an orifice that opens and closes inresponse to differential pressure across the valve; a screen secured tothe valve housing and covering the orifice, the screen having a finemess for removing contaminants from the fluid that flows through thevalve.
 2. The filter assembly of claim 1, further comprising a channelformed in the filter housing that includes: a second inlet communicatingwith the chamber and located adjacent the valve; a second outletcommunicating with the outlet of the valve housing; and a lengthconnecting the second inlet and second outlet, the channel increasing inelevation as distance from the second inlet along the channel lengthincreases.
 3. The filter assembly of claim 1, further comprising achannel formed in the filter housing that includes: a second inletlocated adjacent the valve; a second outlet communicating with theoutlet of the valve housing; a length connecting the second inlet andsecond outlet; and a depth that increases along the channel length, thechannel increasing in elevation as distance from the second inlet alongthe channel length increases.
 4. The filter assembly of claim 1, furthercomprising: a filtration element located in the filter housing andextending from the valve toward the housing outlet.
 5. The filterassembly of claim 1, wherein the valve housing further comprises: avalve seat; an orifice formed in the valve seat; a ball moveably intocontact with the valve seat to close the orifice, and out of contactwith the valve seat to open the orifice; and a spring for urging theball toward contact with the valve seat.
 6. The filter assembly of claim1, wherein the valve housing further comprises: a valve seat; an orificeformed in the valve seat; a ball moveably into contact with the valveseat to close the orifice, and out of contact with the valve seat toopen the orifice; a spring for urging the ball toward contact with thevalve seat; and ribs for supporting the screen.
 7. The filter assemblyof claim 1, wherein the valve housing further comprises: a valve seat;an orifice formed in the valve seat; a ball moveably into contact withthe valve seat to close the orifice, and out of contact with the valveseat to open the orifice; a spring for urging the ball toward contactwith the valve seat. a valve cavity located at a lower elevation than anelevation of the orifice, the valve housing being formed with a hole forcommunicating the valve cavity with an exterior of the valve housing,the hole being located at a higher elevation than the elevation of theorifice.
 8. A filter assembly for an automatic transmission, comprisinga filter housing including an inlet, through which hydraulic fluidenters the housing, an outlet, through which hydraulic fluid exits thehousing, and a channel that includes a second inlet communicating withthe chamber, a second outlet communicating with the outlet of the valvehousing, and a length connecting the second inlet and second outlet, thechannel increasing in elevation as distance from the second inlet alongthe channel length increases; and valve housing containing a bypassvalve located adjacent the inlet in a chamber, the valve including anorifice that opens and closes in response to differential pressureacross the valve;
 9. The filter assembly of claim 8 further comprising:a screen in the form of a dome supported by ribs secured to the valvehousing, the screen including a mesh covering the orifice for removingcontaminants from the fluid that flows through the valve.
 10. The filterassembly of claim 8, wherein the channel further includes a depth thatincreases along the channel length, the channel increasing in elevationas distance from the second inlet along the channel length increases.11. The filter assembly of claim 8, further comprising: a filtrationelement located in the filter housing and extending from the valvetoward the housing outlet.
 12. The filter assembly of claim 8, whereinthe valve housing further comprises: a valve seat formed with theorifice; a ball moveably into contact with the valve seat to close theorifice, and out of contact with the valve seat to open the orifice; anda spring for urging the ball toward contact with the valve seat.
 13. Thefilter assembly of claim 8, wherein the valve housing further comprises:a valve seat formed with the orifice; a ball moveably into contact withthe valve seat to close the orifice, and out of contact with the valveseat to open the orifice; a spring for urging the ball toward contactwith the valve seat; and ribs for supporting the screen.
 14. The filterassembly of claim 8, wherein the valve housing further comprises: avalve seat formed with the orifice; a ball moveably into contact withthe valve seat to close the orifice, and out of contact with the valveseat to open the orifice; a spring for urging the ball toward contactwith the valve seat. a valve cavity located at a lower elevation than anelevation of the orifice, the valve housing being formed with a hole forcommunicating the valve cavity with an exterior of the valve housing,the hole being located at a higher elevation than the elevation of theorifice.